add last version
testing, issue #1104: Make the test use static flags
add websocket support to /container/<name>/attach/ws

This function add the possibility to attach containers streams to a
websocket. When a websocket is asked the request is upgraded to this
protocol..
change tag -> repo name in build usage
Added version checker interface
inserted setUserAgent in each HTTP request
added APIVersion when call NewRegistry
Insert version checkers when call NewRegistry()
added client's kernel version
Removed an unnecessary error check.
Removed an unnecessary nil assignment
format in the user agent header should follow RFC 2616
reduce the number of string copy operations.
use http://get.docker.io/latest
put the websocket route in the map containing all routes

Instead of handling the websocket differently just handle it as a normal
route and upgrade it to a websocket.
useless type
useless function. forgot to remove it.
reuse the type
docker.upstart: avoid spawning a `sh` process

start script / end script create an intermediate sh process.
docker.upstart: use the same start/stop events as sshd

Is probably more solid